a certain galaxies and the distance it is speeding from us. once you have a relation between the distance and the speed, and the relation, but the way, is linear so if something is more distant, it moves faster from us -- once you have a relation like this, you can roll it back, like a video that you run backward, and you can discover when it did the expected start. if i tell you that the distance from here to baltimore is -- i don't know what it is -- 40 miles, let's say, it will take you an hour to get there. of course, it never does, because the parkway is always full of repairs and things, but that is a different question. in this particular case, you can use this to roll the movie of the universe back and discover how old are universe is. the problem is, in astronomy, while you can determine speeds relatively easy, because you use something that is similar to the doppler effect, this thing that when something moves away, waves gets spread out, so you can, by seeing how waves gets spread out, it tell how fast it is moving, distances are very difficult to tell in astronomy. you look to
